PROJECT SUMMARY Newborn screening for Fabry, Gaucher, Niemann Pick Types A and B, and Pompe diseases has been proposed in several states, including New York. Each of these lysosomal storage diseases (LSD) has a broad phenotypic spectrum ranging from severe infantile-onset disease to adult-onset, milder phenotypes. Thus, newborn screening for these disorders presents a unique set of complex issues that require investigation prior to the initiatio of mass newborn screening. These issues include determining the clinical and diagnostic accuracy of the screening assay, investigating how to correctly predict phenotype in asymptomatic newborns, and developing algorithms to assist with clinical decision-making about if and when to initiate therapy. In addition, there are novel ethical, legal, and social issus associated with testing infants for potentially later-onset disorders. This proposal will explore these issues by implementing a pilot newborn screen in conjunction with the New York State Newborn Screening Program to evaluate the analytic and clinical validity of the screening test and to determine disease incidence in an ethnically diverse population. Screening data will be shared with the Newborn Screening Translational Research Network (NBSTRN). All identified infants will be followed by LSD experts at The Mount Sinai Medical Center for diagnostic evaluation, monitoring, and treatment. Natural history data generated from this research and from existing disease-specific clinical databases will also be shared with the NBSTRN, with the goal of developing models to predict age of onset of disease over the lifespan in order to optimize treatment and avoid premature use of costly therapies. The psychological aspects of screening for the LSDs will also be explored, focusing on whether screening for later-onset disorders has harmful short or longer term effects. The psychological impact will be assessed using questionnaires and interviews to evaluate the reactions of parents whose infants are at risk to develop infantile versus later-onset disease. We will also initiate an analysis of the economic impact of a positive diagnosis on families by analyzing monitoring and treatment costs as well as potential difficulties with insurability. Based on these results, an ethics panel will b convened to discuss the particular concerns, including potential harms, that are associated with testing for these disorders, and we will then use this information as the basis for formulating policy recommendations on newborn screening for LSDs in general, and later onset diseases in particular. In addition, a symposium will be held to discuss the extent and length of medicolegal responsibility of the medical team involved in the newborn screening of a patient with adult onset disease. In sum, these studies should result in the development of evidence-based, ethically-sensitive, newborn screening and long-term follow up policies that will have considerable influence as newborn screening for the LSDs becomes widely adopted.